A mechanical coolant pump is a coolant pump which is driven by a combustion engine, for example, by using a driving belt driving a driving wheel of the pump. As long as the combustion engine is cold, only a minimum or even no coolant flow is needed. witchable mechanical coolant pumps are therefore used which are provided with a friction clutch for coupling or decoupling the driving wheel with the shaft holding the pump wheel which is pumping the coolant.
The switchable coolant pump comprises a first roller bearing supporting the driving wheel at a stationary cylindrical supporting body and comprises a second rotor bearing supporting the rotatable shaft of the pump wheel. In practice, ready-made roller bearings are used which are press-fit onto the respective parts of the coolant pump. The press fitting process requires a highly accurate production of the corresponding cylindrical parts the coolant pump, i.e., of the inner and outer cylindrical surfaces of the stationary cylindrical supporting body, the outer surface of the rotating shaft and the inner surface of the driving wheel. The press fitting process is also a sophisticated process which causes a high assembly effort.
Even if the two roller bearings are not arranged radially in line, but are arranged axially in line, the outer diameter of the driving wheel is, in practice, higher than 9-10 centimeters.
For combustion engines with a relatively low displacement compact, coolant pumps with a relatively low outer diameter of the driving wheel are needed.